Quantitative Vestibular Labyrinthine Otopathology in Temporal Bones with Vestibular Schwannoma.

OBJECTIVE Dizziness associated with vestibular schwannoma is usually ascribed to retrolabyrinthine mechanisms. The goal of this study was to determine if quantitative peripheral vestibular (labyrinthine) otopathology was present in a series of patients with vestibular schwannoma. STUDY DESIGN Comparative human temporal bone study. SETTING Otopathology laboratory. SUBJECTS AND METHODS Temporal bones from 12 subjects with unilateral sporadic vestibular schwannoma were included. Based on differential interference contrast microscopy, type I and II vestibular hair cell counts were performed on each vestibular sense organ with minimal autolysis in which the neuroepithelium was oriented perpendicular to the plane of section. Hair cell densities (cells per 0.01-mm(2) surface area) and the presence of endolymphatic hydrops and precipitate within the endolymph or perilymph were compared between the tumor ears and the contralateral (control) ears. RESULTS Compared with the contralateral ears, vestibular schwannoma ears had significantly more endolymphatic hydrops (P = .049) and precipitate in the endolymph and perilymph (P = .005), lower densities of type I and II vestibular hair cells in the lateral canal cristae (mean differences, respectively: 25.2 [P = .001] and 10.8 [P < .001]) and utricle (mean differences, respectively: 26.8 and 10.4 [P < .001]), and lower densities of type I hair cells and the same density of type II hair cells in the saccule (mean differences, respectively: 26.5 [P < .001] and 0.9 [P = .46]). CONCLUSION Peripheral vestibular otopathology, manifested as reductions of vestibular hair cell densities, was identified in ears with vestibular schwannoma. Labyrinthine as well as retrolabyrinthine pathology may contribute to tumor-related vestibular dysfunction.